1. Field of the Invention
This invention relates to a respiratory mask for use with a non-invasive positive pressure ventilation device and headgear for use with such a respiratory mask, and a frame to allow connection of a respiratory mask to the headgear.
2. General Background and Related Art
Non-invasive positive pressure ventilation (NIPPV) techniques, such as, for example, the application of continuous positive airway pressure (CPAP), have been used for the treatment of Sleep Disordered Breathing (SDB), such as Obstructive Sleep Apnea (OSA). An apparatus for applying NIPPV typically comprise a blower, an air delivery conduit, and a patient interface. A number of different patient interfaces are known, such as nasal masks, nose and mouth masks, full face masks, and nasal prongs or pillows. In all cases, some form of mask retaining feature, such as a headgear, is required to position the mask on the face and to counterbalance the force which results from the application of pressurized air that seeks to push the mask off the face.
A nasal mask typically comprises a generally triangularly shaped chamber constructed from a relatively rigid material, such as polycarbonate, with an open side that, when in use, is positioned against the face. The edge of the open side typically includes a cushion that helps form a seal on the patient's face. The cushion is typically soft to facilitate patient comfort. It is important that there be a good seal with few leaks because leaks can compromise therapy, e.g., cause air jetting and noise, which may be uncomfortable for the patient and cause improper functioning of the blower. Patient comfort is important since the patient must sleep while wearing the mask.
Prior art masks have typically been fairly uncomfortable for the patient. Previously, the masks themselves were uncomfortable due to a relatively small surface area (i.e., contacting area) of the cushion and an insubstantial degree of flexibility of the cushion. However, there have been advances in the design of masks, which have increased the surface area and the flexibility of the cushion. Therefore, the masks themselves have been improved in design so as to allow relatively comfortable engagement with the face. However, there remains a deficiency in the art to hold the mask to the patient's face in a manner that is comfortable for the patient for all pressures delivered to the mask.
In particular, previous designs of headgear that connect to the mask to hold the mask to the face, have utilized flexible straps which generally wrap around the head and connect to the mask (or a frame connected to the mask). The straps of the headgear are constructed of elastic, extensible material to increase patient comfort. However, the elasticity of the straps requires the mask to be strapped to the patient's face with an uncomfortable pressure. This is because the mask must be held to the face with strap tension sufficient to prevent leaks of air between the cushion and the face when the blower delivers a high pressure of air to the mask. The straps may be adjusted so that the residual elastic force in the straps is negligible to decrease the pressure applied to the face by the mask. However, this may be insufficient to hold the mask to the face during high pressure air delivery with sufficient force to prevent leaks. Even if no leaks are present, the mask may be caused to lift away from the face due to the high pressure of air, which reactively stretches the straps of the headgear. After lifting away, the elasticity of the straps causes the mask to recoil against the face upon cessation of the high pressure air delivery.
Stated differently, in the case of use with a varying air pressure source such as a ventilator or automatic CPAP device, or a CPAP device with an initial pressure ramp, if the straps are done up or tensioned sufficiently tight to seal at high pressure, there will be unnecessary excess force on the face at low pressure. Conversely, if the straps are done up or tensioned enough to just seal at low pressure, the mask will lift off the face and leak at high pressure.
Additionally, elastic straps of previous headgear designs have a tendency to wander or slide about the patient's head when the patient moves during sleep. This sliding of the headgear may cause headgear tension vectors to move away from their optimal position giving rise to leak and/or discomfort.
Furthermore, straps of prior art headgear have typically not been designed to allow both precise and easy adjustment. Therefore, the straps and adjustment of them were relatively cumbersome to the patient. Additionally, the elastic and pliable straps tend to flop and tangle when donning the headgear. Moreover, many designs required the patient to refit the headgear every time the headgear was removed and subsequently put back on.
Other drawbacks of the prior art relate to the connection of the headgear to the mask itself. This connection is accomplished either by clips attached directly to the mask and the straps of the headgear, or by use of a frame. Typical frames are connected to the mask and have connection points or clips thereon to allow connection of straps of the headgear. Typically, one or more connections of straps to the frame were of a quick release type to allow emergency removal of the mask. However, previous designs for frames have required additional componentry which increases costs of the mask/headgear assembly and/or have required some form of forehead support. Additional contact of the frame with the face may decrease the degree of comfort for the patient.